In diagnosing arrhythmias, diagnostically relevant information includes a type of arrhythmia and a rate during the arrhythmia, as well as a patient's symptoms, activity level, and posture before and after the arrhythmia. While cardiac monitors may be utilized to detect various types of arrhythmias and a patient's rate during the arrhythmia, current monitors fail to provide accelerometer-derived objective patient activity levels and posture before and after an arrhythmia. Generally, this is because cardiac monitoring—particularly ambulatory monitoring—includes long-term monitoring of ECG signals and the amount of data generated by an accelerometer in an ambulatory setting is cost prohibitive with respect to transmission costs and battery longevity, among other things. Instead, physicians and other medical professionals either rely on the patient to record symptoms and activity levels in a patient diary, or the patient's recollection of symptoms and activity levels at a later date, for example, during an examination or a phone call from the monitoring center to note symptoms when the patient trigger is pressed. While in some instances a time of day at which an arrhythmia occurred is relied upon to estimate a patient's activity level and/or posture, time of day is a poor surrogate for activity information recorded in real-time.
Current devices that monitor patient activity could also suffer from errors due to the location of the device being on a periphery of the patient, such as an arm or wrist. For example, current devices may monitor patient activity via hand-only movement, but this introduces error, distorts signals, and sacrifices accuracy. Furthermore, current devices that attach to an article of clothing (e.g., a belt clip/holster or lanyard) do not provide reliable measurements of patient activity since they are not adhered to nor implanted in a patient's body. In addition, utilization of independent devices for monitoring patient activity and ECG, respectively, without a shared common clock, could result in problems synchronizing detected activity levels and arrhythmias.
It would therefore be desirable to provide a system and method that may be adhered to or implanted in a patient's body, reduce the amount of accelerometer data needed to continuously track and accurately detect a patient's activity and posture, and synchronize results with one another to enhance a diagnosis of arrhythmia.